Theoretical and experimental investigation of Kramers-Henneberger states in alkaline and noble gas atoms

碱性和稀有气体原子中 Kramers-Henneberger 态的理论和实验研究

• 批准号: 281309735
• 负责人: Professor Dr. Mikhail Ivanov
• 金额: --
• 依托单位: Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (MBI)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/281309735?language=en
• 关键词: Theoretical; experimental; investigation; Kramers; Henneberger

The main objective of this project is to provide direct spectroscopic evidence for the bound states of a free electron an unusual quantum state created by the concerted actionof the attractive core potential and a strong laser field. Electrons in such states respond to the laser field almost like free electrons, yet on average they remain bound to the ionic core. The states are often referred to as the Kramers-Henneberger (KH) states, after first theoretical predictions made about 50 years ago. For many decades, the KH states looked like a purely theoretical concept of academic interest. However, today there is mounting indirect experimental evidence suggesting that these states are ubiquitous and can emerge almost any time an atom or a molecule is exposed to sufficiently intense infrared laser fields. The combined action of the attractive core potential and the laser electric field creates a potential barrier through which a bound electron can escape. As the laser intensity increases, the top of the potential barrier can descend below the energy of a bound electronic state. Yet, the state does not necessarily become free. While the electron oscillation amplitude in such a state reaches some ten angstroms, it remains stable against ionization. Crucially, this situation is typical for all excited atomic states exposed to infrared laser fields with intensities in mid-1013 W/cm2 and higher. Such restructuring of the atomic spectrum has important implications for nonlinear light-matter interaction, including such processes as laser filamentation. The emergence of Kramers-Henneberger states inside a laser filament is extremely likely, and their role in the filamentation process can be substantial. One of the key goals of our project is to investigate the emergence of these states, their role in the filamentation process, and provide conclusive, direct spectroscopic evidence of their existence. Our goal is to provide two complementary spectroscopic observations, based on angle-resolved photo-electron spectroscopy of isolated atoms and transient absorption spectroscopy in laser filaments, to resolve this intriguing situation.

该项目的主要目标是为自由电子的束缚态提供直接的光谱证据，这是由有吸引力的核心势和强激光场的协同作用产生的不寻常的量子态。这种状态下的电子几乎像自由电子一样对激光场作出响应，但平均而言，它们仍然与离子核心结合。在大约 50 年前做出首次理论预测之后，这些状态通常被称为克拉默斯-亨内伯格 (KH) 状态。几十年来，KH 状态看起来像是一个纯粹的学术兴趣理论概念。然而，如今越来越多的间接实验证据表明，这些状态无处不在，并且几乎在原子或分子暴露于足够强的红外激光场时就会出现。有吸引力的核心电势和激光电场的联合作用产生了势垒，束缚电子可以通过该势垒逃逸。随着激光强度的增加，势垒的顶部可以下降到束缚电子态的能量以下。然而，国家并不一定会变得自由。虽然这种状态下的电子振荡幅度达到约十埃，但它仍能保持稳定的电离状态。至关重要的是，这种情况对于暴露于强度为 1013 W/cm2 及以上的红外激光场的所有激发原子态来说都是典型的。原子光谱的这种重组对于非线性光与物质相互作用具有重要意义，包括激光成丝等过程。激光灯丝内部极有可能出现克莱默-亨内伯格态，并且它们在成丝过程中的作用可能很大。我们项目的主要目标之一是研究这些状态的出现、它们在丝化过程中的作用，并提供它们存在的结论性的、直接的光谱证据。我们的目标是提供两种互补的光谱观测，基于孤立原子的角分辨光电子能谱和激光灯丝中的瞬态吸收光谱，以解决这一有趣的情况。